It is successor of most famous DOS Spectrum emulator Z80. As DOS
versions, Win version was shareware too, but now you may get full,
unrestricted versions (Win & DOS in one pack) from author's
homesite (not emulator oriented). 6 years later it is still very
usable, however best to run in Win 98. Code is very efficient, and it
works very fast even on slow machines. On Pentium 200 MHz it can achieve
over 2000% speed of real Spectrum. List of emulated models is not big,
but there is lot of peripherals:

Double sized window (here at 50%):

Feature list is really big, in DOS version directory you may find some
useful utilities for diverse conversions. There is even audio mixer:

Maybe only thing what is missing is true multicolor (contended memory)
emulation. Of course, most of games requires it not. Programm is
recommended for owners of older PC's, DOS or Win 95/98. There is
option for video recording, in format of 'WEB-friendly' animated GIF
:-) :